1. Field of the Invention
The present invention relates generally to an image forming apparatus, and more particularly to a relatively large-size copying machine including, for example, an auto document feeder for automatically feeding a document to a copying operation start position, and a sorter for grouping or stacking image-reproduce documents.
2. Description of the Related Art
A conventional large-size copying machine designed to enhance the copying operation efficiency is provided with, for example, an auto document feeder (ADF) and a sorter. A user sets originals in the copying machine and inputs data of copying conditions such as the desired number of copies, the reproduction magnification, the grouping/stacking modes, etc. Then, the user turns on a start key. Thus, hard copies which meet the copying conditions can be obtained.
Instead of the ADF, a return auto document feeder (RADF) is also provided in the large-size copying machine. The RADF is capable of automatically reversing an original document, thereby making it possible to reproduce image information on both sides of the document.
An example of the sorter is a coupling type sorter capable of grouping or stacking all reproduced copies by a single operation, even if the number of reproduced copies is large. Normally, a sorter has 5 to 20 storage sections (called "bin") for grouping or stacking. When the number of copies to be reproduced is greater than the number of storage sections, the storage sections are coupled in series (named "coupling type sorter") thereby substantially increasing the number of storage sections.
In the above copying machines with the RADF and coupling type sorter, however, a first copying operation (two or more hard copies are obtained from two or more the RADF and coupling type sorter, however, a first copying operation (two or more hard copies are obtained from two or more originals) cannot be interrupted by a second copying operation (two or more hard copies are obtained from two or more originals). In other words, when the first copying operation is interrupted by the second copying operation, it is necessary to suspend the first copying operation and start the second copying operation and, after the completion of the second copying operation, resume the first copying operation.
Under this situation, the user is unable to fully enjoy the advantages of the expensive large-size copying machine. While the first copying operation, which is to be carried out quickly, is continued, the interruption of the second copying operation is, in fact, disabled. The fact that the interruption of the second copying operation is substantially disabled results in an increase in copying costs.